Methods and Systems for Increasing Sensitivity of Direct Sampling Interfaces for Mass Spectrometric Analysis

ABSTRACT

Methods and systems for delivering a liquid sample to an ion source for the generation of ions and subsequent analysis by mass spectrometry are provided herein. In accordance with various aspects of the present teachings, MS-based systems and methods are provided in which the flow of desorption solvent within a sampling probe fluidly coupled to an ion source can be selectively controlled such that one or more analyte species can be desorbed from a sample substrate inserted within the sampling probe within a decreased volume of desorption solvent for subsequently delivery to the ion source. In various aspects, sensitivity can be increased due to higher desorption efficiency (e.g., due to increased desorption time) and/or decreased dilution of the desorbed analytes. The methods and systems described herein can additionally or alternatively provide for the selective control of the flow rate of the desorption solvent within the sampling interface so as to enable additional processing steps to occur within the sampling probe (e.g., multiple samplings, reactions).

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/341,718, filed on Apr. 12, 2019, which is a national stageapplication, filed under 35 U.S.C. 371 of International PatentApplication no. PCT/IB2017/056335, filed on Oct. 12, 2017, which claimsthe benefit of priority from U.S. Provisional Application Ser. No.62/408,454, filed on Oct. 14, 2016, the entire contents of all of whichare hereby incorporated by reference.

FIELD

The present teachings generally relate to mass spectrometry, and moreparticularly, to sampling interfaces for mass spectrometry systems andmethods.

INTRODUCTION

Mass spectrometry (MS) is an analytical technique for determining theelemental composition of test substances with both qualitative andquantitative applications. MS can be useful for identifying unknowncompounds, determining the isotopic composition of elements in amolecule, determining the structure of a particular compound byobserving its fragmentation, and quantifying the amount of a particularcompound in a sample. Given its sensitivity and selectivity, MS isparticularly important in life science applications.

In the analysis of complex sample matrices (e.g., biological,environmental, and food samples), many current MS techniques requireextensive pre-treatment steps to be performed on the sample prior to MSdetection/analysis of the analyte of interest. Such pre-analytical stepscan include sampling (i.e., sample collection) and sample preparation(separation from the matrix, concentration, fractionation and, ifnecessary, derivatization). It has been estimated, for example, thatmore than 80% of the time of overall analytical process can be spent onsample collection and preparation in order to enable the analyte'sdetection via MS or to remove potential sources of interferencecontained within the sample matrix, while nonetheless increasingpotential sources of dilution and/or error at each sample preparationstage.

Ideally, sample preparation and sample introduction techniques for MSshould be fast, reliable, reproducible, inexpensive, and in someaspects, amenable to automation. One recent example of an improvedsample preparation technique is solid-phase microextraction (SPME),which essentially integrates sampling, sample preparation, andextraction into a single solvent-free step. Generally, SPME devicesutilize a fiber or other surface (e.g., blades, micro-tips, pins, ormesh) coated with an extracting phase to which analytes within thesample can be preferentially adsorbed when the device is inserted intothe sample. Because extraction can take place in situ by inserting abiocompatible device directly into tissue, blood, or other biologicalmatrix for a short period of time, SPME does not require any samplecollection. Alternatively, SPME devices can be used for ex vivo analysisusing a small amount of a collected sample (i.e., a sample aliquot).

Though SPME is generally considered to be accurate and simple and canresult in decreased sample preparation time and disposal costs, themass-spectrometric based analysis of

SPME-prepared samples may nonetheless require additional equipmentand/or time-consuming steps in order to ionize the analyte from the SPMEdevice directly or to desorb the analytes from the SPME device prior toionization as required for mass spectrometry (MS). By way of example,various ionization methods have been developed that can desorb/ionizeanalytes from condensed-phase samples with minimal sample handling(e.g., desorption electrospray ionization (DESI) and direct analysis inreal time (DART), which “wipe-off” analytes from the samples by exposingtheir surfaces to an ionizing medium such as a gas or an aerosol).However, such techniques can also require sophisticated and costlyequipment, and may be amenable only for a limited class ofhighly-volatile small molecules.

Alternatively, additional desorption steps have been utilized to extractthe analytes from the SPME device prior to ionization via ionizationtechniques other than DESI or DART. For example, because electrosprayionization (ESI) is one of the most common ionization methods andrequires the analyte to be in solution, some users have utilized liquiddesorption and subsequent purification/separation of theextracted/enriched analytes via high-performance liquid chromatography(HPLC) prior to MS analysis. However, liquid desorption prior to HPLCmay require an extended processing step to transfer the analyte from theSPME coating to a relatively large volume liquid phase due torequirements imposed on the HPLC mobile phase (e.g., a weak solventstrength), can decrease throughput, introduce potential sources oferror, increase dilution, and cannot be easily automated. Some groupshave instead proposed substantial modifications to the standardelectrospray ion source itself. Typically in ESI, a liquid sample iscontinuously discharged into an ionization chamber from within anelectrically conductive capillary, while an electric potentialdifference between the capillary and a counter electrode generates astrong electric field within the ionization chamber that electricallycharges the liquid sample. This electric field causes the liquiddischarged from the capillary to disperse into a plurality of chargedmicro-droplets drawn toward the counter electrode if the charge imposedon the liquid's surface is strong enough to overcome the surface tensionof the liquid (i.e., the particles attempt to disperse the charge andreturn to a lower energy state). As solvent within the micro-dropletsevaporates during desolvation in the ionization chamber, charged analyteions can then enter a sampling orifice of the counter electrode forsubsequent mass spectrometric analysis. PCT Pub. No. WO2015188282entitled “A Probe For Extraction Of Molecules Of Interest From ASample,” which is incorporated by reference herein in its entirety, forexample, thus purports to provide for electrospray ionization from anSPME device by applying the ionizing electric potential to theconductive SPME device itself (to which a discrete amount of adesorption solution is applied) such that ions are generated directlyfrom the edges of the wetted substrate.

There remains a need for improved and/or reduced-cost systems thatenable fast-coupling of SPME devices to MS systems with minimalalterations to the front-end while maintaining sensitivity, simplicity,selectivity, speed and throughput.

SUMMARY

Methods and systems for delivering a liquid sample to an ion source forthe generation of ions and subsequent analysis by mass spectrometry areprovided herein. In accordance with various aspects of the presentteachings, MS-based systems and methods are provided in which the flowof desorption solvent within a sampling probe fluidly coupled to an ionsource can be selectively stopped such that the one or more analytespecies desorbed from a sampling substrate (e.g., substrates havingfunctionalized surfaces, an SPME substrate, surface-coated magneticparticles) are concentrated in a decreased volume of the desorptionsolvent that is subsequently delivered via one or more fluid pathways tothe ion source, thereby decreasing dilution of the desorbed analytes andincreasing the sensitivity of detection of the desorbed analytes. Invarious aspects, the analytes from the SPME device can be desorbedtherefrom by increased concentration of desorption solvent and/orwithout a liquid chromatography (LC) column between the desorptionsampling interface and the ion source. Additionally or alternatively,various aspects of the present teachings provide for the selectivecontrol of the flow rate of the desorption solvent within the samplinginterface so as to enable additional processing steps (e.g., multiplesamplings, reactions) within the sampling interface. In accordance withvarious aspects of the present teachings, desorption solvent can becontinuously delivered to the ion source during the stopped-flowcondition of the sampling interface so as to maintain the stability ofthe one or more pumping mechanisms and the ion spray source.

In accordance with various exemplary aspects of the present teachings, asystem for analyzing a chemical composition of a specimen is provided,the system comprising a reservoir for storing a desorption solvent and asampling probe having an open end at least partially defining a samplespace configured to receive desorption solvent from the reservoir, thesample space being further configured to receive at a least a portion ofa substrate having one or more analyte species adsorbed thereto suchthat at least a portion of said analyte species can be desorbedtherefrom into the desorption solvent within the sample space. Thesystem additionally includes a plurality of fluid pathways fordelivering desorption solvent from the reservoir to an ion source and afluid handling system alternately providing a first fluid pathway forflowing desorption solvent from said reservoir to said ion source viasaid sample space, and a second fluid pathway that bypasses said samplespace while flowing the desorption solvent from said reservoir to saidion source. In some aspects, for example, the fluid handling system cancomprise a valve movable between a first configuration and a secondconfiguration, wherein in the first configuration the first fluidpathway is provided for flowing desorption solvent from the reservoir tothe ion source via the sample space, and wherein in the secondconfiguration the second fluid pathway is provided for flowing thedesorption solvent from the reservoir to the ion source while bypassingthe sample space. In certain aspects, the desorption solvent can bedelivered to the ion source substantially continuously when the valve isin each of the first and second configuration. Additionally, in someaspects, the volumetric flow rate of the desorption solvent in thesample space is substantially zero in the second configuration.Moreover, in some aspects, the volumetric flow rate of the desorptionsolvent from the reservoir to the ion source is substantially zero forportions of time in the second configuration.

The valve can have a variety of configurations in accordance with thepresent teachings. By way of example, in some aspects the valve cancomprise a first port fluidly coupled via a first fluid channel to anoutlet of the reservoir; a second port fluidly coupled via a secondfluid channel to an inlet end of the sampling probe; a third portfluidly coupled via a third fluid channel to an outlet end of thesampling probe; and a fourth port fluidly coupled via a fourth fluidchannel to an inlet of the ion source. In some related aspects, thefirst fluid pathway can comprise the first, second, third, and fourthfluid channels and the second fluid pathway can comprise the first andfourth fluid channels. In various exemplary aspects, the valve cancomprise first and second passages, wherein in the first configuration,the first passage fluidly couples the first and second ports and thesecond passage fluidly couples the third and fourth ports, and in thesecond configuration, the first and second passages can be actuated(e.g., rotated, manually or electrically under the control of acontroller) such that the first passage fluidly couples the first andfourth ports and the second passage fluidly couples the second and thirdports. Alternatively, in some aspects, the first passage fluidly couplesthe first and second ports and the second passage fluidly couples thethird and fourth ports in the first configuration, and wherein in thesecond configuration, the first and second passages are actuated (e.g.,rotated, manually or electrically under the control of a controller forexample) such that the first passage fluidly couples the second andthird ports and the second passage fluidly couples the first and fourthports.

The sampling probe can have a variety of configurations. By way ofexample, in some exemplary aspects, the probe can comprise an outercapillary tube extending from a proximal end to a distal end and aninner capillary tube extending from a proximal end to a distal end andat least partially disposed within the outer capillary tube. In certainaspects, the distal end of the inner capillary tube can be recessedrelative to the distal end of the outer capillary tube so as to definethe sample space between the distal end of the inner capillary tube, aportion of an inner wall of the outer capillary tube, and the distal endof the outer capillary tube. Further, the inner and outer capillarytubes can define a desorption solvent conduit and a sampling conduit influid communication with one another via the sample space, thedesorption solvent conduit extending from an inlet end configured toreceive desorption solvent from the reservoir to an outlet endterminating at the sample space, and the sampling conduit extending froman inlet end commencing at said sample space for receiving from thesample space desorption solvent in which the desorbed analytes areentrained to an outlet end fluidly coupled to the ion source.

In some related aspects, an axial bore of the inner capillary tube atleast partially defines the sampling conduit and a space between theinner capillary tube and the outer capillary tube defines the desorptionsolvent conduit, and further wherein the inlet end of the desorptionsolvent conduit is disposed in the first fluid pathway between the valveand the sample space and the outlet end of the sampling conduit isdisposed in the first fluid pathway between the sample space and thevalve.

In various aspects, the system can further comprise an ion source fordischarging desorption solvent having the desorbed analytes entrainedtherein into an ionization chamber in fluid communication with asampling orifice of a mass spectrometer.

In some aspects, the system can also comprise a controller forcontrolling movement of the valve between the first and secondconfigurations, the controller configured to move the valve to thesecond configuration for insertion of the substrate within desorptionsolvent within the sample space. Additionally, the controller caneffectuate the actuation of the valve so as to move the valve to thefirst configuration for flowing desorption solvent having analytesdesorbed therein from the sample space to the ion source, whereindesorption solvent is delivered to the ion source substantiallycontinuously when the switch is in each of the first and secondconfiguration. In some related aspects, the system can further compriseone or more pumps for flowing desorption solvent through the first andsecond pathways, the controller configured to control the flow rate ofdesorption solvent delivered by the one or more pumps such thatdesorption solvent forms a dome-like surface profile at the open endwhen the valve is moved to the second configuration and a vortex-shapedsurface at the open end when the valve is moved to the firstconfiguration. In additional related aspects, the controller can befurther configured to control the flow rate of desorption solventdelivered by the one or more pumps such that desorption solventtemporarily overflows from the sample space through the open end of thesampling probe when the valve is in the first configuration so as to atleast one of clean the sampling probe and prevent sampling of airbornematerial before the substrate is inserted within the desorption solvent.

In accordance with various exemplary aspects of the present teachings, amethod for analyzing a chemical composition of a specimen is provided,the method comprising inserting at least a portion of a substrate havingone or more analytes adsorbed thereto (e.g., a SPME substrate having asurface coated with an extraction phase) into a desorption solventcontained within a sample space of a sampling probe for a first durationsuch that at least a portion of said absorbed analytes are desorbed fromthe coated surface into the desorption solvent, said sample space beingpartially defined by an open end of the sampling probe. In variousaspects, the first duration can be in the range of from about 1 secondto about 5 minutes, by way of non-limiting example. The method canfurther comprise directing a flow of the desorption solvent from areservoir of the desorption solvent to an ion source while bypassing thesample space during at least a portion of said first duration such thatthe volumetric flow rate of the desorption solvent in the sample spaceis substantially zero. Thereafter, the flow of desorption solvent fromthe reservoir to the ion source can be re-directed via the sample spacesuch that the analytes desorbed into the desorption solvent within thesample space are delivered to the ion source. The desorbed analytesentrained within the desorption solvent can then be ionized by the ionsource for mass spectrometric analysis. In various aspects, a valvemovable between a first configuration and a second configuration fordirecting the flow of desorption solvent through a plurality of fluidpathways is disposed between the reservoir and the sample space, andwherein re-directing the flow of desorption solvent from the reservoirto the ion source via the sample space comprises actuating the valvefrom the first configuration to the second configuration. In certainaspects, the desorption solvent can be delivered to the ion sourcesubstantially continuously when the valve is in each of the first andsecond configuration. Additionally, in some aspects, the volumetric flowrate of the desorption solvent in the sample space is substantially zeroin the second configuration. In some related aspects, a first fluidpathway is provided for flowing desorption solvent from the reservoir tothe ion source via the sample space and a second fluid pathway isprovided for flowing the desorption solvent from the reservoir to theion source and that bypasses the sample space.

In various aspects, the method can further comprise establishing theflow of the desorption solvent through the sample space prior toinserting said substrate within the sample space, wherein a flow rate ofthe desorption solvent within the sample space is configured to generatea dome-like surface profile of the desorption solvent at said open endwhen the substrate is inserted therein; and adjusting the flow rate ofthe desorption solvent within the sample space during said step ofre-directing the flow of desorption solvent from the reservoir to theion source via the sample space so as to generate a vortex-like surfaceprofile of the desorption solvent at said open end. Additionally oralternatively, the method can include setting a flow rate of desorptionwithin said sample space such that desorption solvent overflows from thesample space through the open end of the probe prior to inserting thesubstrate so as to at least one of clean the probe and prevent samplingof airborne material.

In various aspects of the present teachings, the method can furthercomprise adding one or more reagents to the sample space during saidfirst duration for reacting with analytes that are at least one ofadsorbed on the substrate and desorbed from the substrate.

In accordance with various exemplary aspects of the present teachings, asystem for analyzing a chemical composition of a specimen is provided,the system comprising a reservoir for storing a desorption solvent and asampling probe having an open end partially defining a sample spaceconfigured to receive desorption solvent from the reservoir, said samplespace further configured to receive through the open end at a least aportion of a substrate having one or more analyte species adsorbedthereto such that at least a portion of said analyte species aredesorbed therefrom into the desorption solvent within the sample space.The system can further comprise a fluid handling system comprising atleast one pump and at least one fluid pathway for delivering desorptionsolvent from the reservoir to an ion source, wherein the fluid handlingsystem is configured to terminate flow of desorption solvent within thesampling space during insertion of the sampling probe therein. Invarious aspects, a controller can be operatively coupled to the at leastone pump and configured to control the volumetric flow rate ofdesorption solvent within the at least one pathway, the controllerconfigured to turn off the pump during insertion of the sampling probe.Additionally or alternatively, in some aspects, the system can furthercomprise a source of nebulizer gas for providing a nebulizing gas flowsurrounding the discharge end of the ion source, wherein the controlleris operatively coupled to the source of nebulizer gas and is configuredto terminate flow of desorption solvent within the sampling space duringinsertion of the sampling probe by terminating the flow of nebulizinggas provided to the discharge end of the ion source. In some exemplaryaspects, the controller can also be configured to increase thevolumetric flow rate of desorption solvent provided to the samplingspace following withdrawal of a first substrate so as to deliver thedesorption solvent having desorbed analytes entrained therein to the ionsource. In various aspects, the controller can additionally oralternatively be configured to actuate the fluid handling system betweena first configuration in which a first fluid pathway is provided forflowing desorption solvent from said reservoir to said ion source viasaid sample space, and a the second configuration in which a secondfluid pathway is provided for flowing the desorption solvent from saidreservoir to said ion source and that bypasses said sample space.

In accordance with various exemplary aspects of the present teachings, asystem for analyzing a chemical composition of a specimen is described,which comprises: a reservoir for storing a delivery solvent; a samplingprobe having an open end partially defining a sample space configured toreceive delivery solvent from the reservoir, said sample space furtherconfigured to receive through the open end one or more liquid dropletshaving one or more analyte species contained therein such that the oneor more liquid droplets is mixable with the delivery solvent within thesample space; a fluid handling system comprising at least one pump andat least one fluid pathway for delivering delivery solvent from thereservoir to an ion source, wherein the fluid handling system isconfigured to terminate flow of delivery solvent within the samplingspace during insertion of the one or more liquid droplets into thesampling space.

In accordance with various exemplary aspects of the present teachings amethod for chemical analysis is described which comprises: inserting oneor more droplets of a liquid sample containing one or more analytes ofinterest into a delivery solvent contained within a sample space of asampling probe for a first duration such that that the one or moredroplets of the liquid sample are mixed with the delivery solvent, saidsample space being partially defined by an open end of the samplingprobe; directing a flow of the delivery solvent from a reservoir of thedelivery solvent to an ion source while bypassing the sample spaceduring at least a portion of said first duration such that thevolumetric flow rate of the delivery solvent in the sample space issubstantially zero; thereafter, re-directing the flow of deliverysolvent from the reservoir to the ion source via said sample space suchthat said one or more droplets of the liquid sample that are mixed withthe delivery solvent within the sample space are delivered to the ionsource; and ionizing the one or more analytes of interest containedwithin the mixed delivery solvent and one or more droplets of liquidsample, for mass spectrometric analysis.

These and other features of the applicant's teachings are set forthherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled person in the art will understand that the drawings,described below, are for illustration purposes only. The drawings arenot intended to limit the scope of the applicant's teachings in any way.

FIG. 1, in a schematic diagram, illustrates an exemplary systemcomprising a substrate sampling interface fluidly coupled to anelectrospray ion source of a mass spectrometer system in accordance withvarious aspects of the applicant's teachings.

FIG. 2, in a schematic diagram, illustrates the exemplary substratesampling interface of FIG. 1 in additional detail, in accordance withvarious aspects of the applicant's teachings.

FIGS. 3A-B schematically depict an exemplary sampling probe for use inthe system of FIG. 1, the sampling probe being operated in a first,continuous flow mode and a second, stopped flow mode, respectively, inaccordance with various aspects of the present teachings.

FIGS. 4A-4D schematically depict exemplary surface shapes of thedesorption solvent in the sample space during the continuous flow modeand the second stopped flow mode, in accordance with various aspects ofthe present teachings.

FIG. 5 depicts in schematic diagram an exemplary automated system forsample analysis in accordance with various aspects of the applicant'spresent teachings.

FIG. 6 depicts in schematic diagram an exemplary embodiment of asampling probe for use in the system of FIG. 1 in which droplets of asample liquid are deposited into a delivery solvent.

DETAILED DESCRIPTION

It will be appreciated that for clarity, the following discussion willexplicate various aspects of embodiments of the applicant's teachings,while omitting certain specific details wherever convenient orappropriate to do so. For example, discussion of like or analogousfeatures in alternative embodiments may be somewhat abbreviated.Well-known ideas or concepts may also for brevity not be discussed inany great detail. The skilled person will recognize that someembodiments of the applicant's teachings may not require certain of thespecifically described details in every implementation, which are setforth herein only to provide a thorough understanding of theembodiments. Similarly it will be apparent that the describedembodiments may be susceptible to alteration or variation according tocommon general knowledge without departing from the scope of thedisclosure. The following detailed description of embodiments is not tobe regarded as limiting the scope of the applicant's teachings in anymanner.

In accordance with various aspects of the applicant's teachings,MS-based analytical systems and methods are provided herein in which theflow of desorption solvent within a sampling probe fluidly coupled to anion source can be selectively controlled (e.g., stopped) such that oneor more analyte species can be desorbed from a sample substrate insertedwithin the sampling probe within a decreased volume of desorptionsolvent for subsequently delivery to the ion source. In various aspects,sensitivity can be increased due to higher desorption efficiency (e.g.,due to increased desorption time) and/or decreased dilution of thedesorbed analytes. In various aspects, the analytes from the samplesubstrate can be desorbed directly therefrom without a liquidchromatography (LC) column between the desorption sampling interface andthe ion source. Additionally or alternatively, various aspects of thepresent teachings provide for the selective control of the flow rate ofthe desorption solvent within the sampling interface so as to enableadditional processing steps to occur within the sampling probe (e.g.,multiple samplings, reactions). In accordance with various aspects ofthe present teachings, desorption solvent can be continuously deliveredto the ion source during the stopped-flow condition of the samplinginterface so as to maintain the stability of the one or more pumpingmechanisms and the ion spray source.

FIG. 1 schematically depicts an embodiment of an exemplary system 10 inaccordance with various aspects of the applicant's teachings forionizing and mass analyzing analytes adsorbed onto the surface of asample substrate 20, the system including a fluid handling system 40that alternately provides first and second fluid pathways for flowingdesorption solvent from a reservoir 50 to an ion source 60 through asampling probe 30 or while bypassing the sampling probe 30,respectively. As shown in FIG. 1, the exemplary system 10 generallyincludes a substrate sampling probe 30 (e.g., an open port probe) influid communication with an ion source 60 for discharging a liquidcontaining one or more sample analytes (e.g., via electrospray electrode64) into an ionization chamber 12, and a mass analyzer 70 in fluidcommunication with the ionization chamber 12 for downstream processingand/or detection of ions generated by the ion source 60. The substratesampling probe 30 can be generally configured to receive at least aportion of the substrate 20 (e.g., an SPME substrate) having a surfacecoated with an extraction phase to which one or more analytes from asample are adsorbed and which is placed in a fluid pathway extendingbetween a desorption solvent source 50, the substrate sampling probe 30,and the ion source 60. In this manner, analytes desorbed from the coatedsurface of the sample substrate 20 can flow within the desorptionsolvent to the ion source 40 for ionization thereby. As will bediscussed in more detail below, the fluid handling system 40 generallycomprises one or more fluidic conduits, valves, and/or pumps forcontrolling the flow of liquid (e.g., desorption solvent) between thereservoir 50, the sampling probe 30, and the ion source 60. In variousaspects, the fluid handling system 40 can be operated (e.g., under thecontrol of a controller, not shown) in a plurality of modes including acontinuous flow mode in which desorption solvent flows from thereservoir 50 to the ion source 60 via the sampling probe 30 and astopped-flow mode in which the desorption solvent from the reservoir 50continues to be delivered to the ion source 60 while bypassing thesampling probe 30. In various aspects, the duration of the stopped-flowmode can be selected to occur during desorption of analytes from one ormore substrates 20 and/or the addition of additional reagents to thesampling probe 30, all by way of non-limiting example.

The ion source 60 can have a variety of configurations but is generallyconfigured to generate analytes contained within a liquid (e.g., thedesorption solvent) that is received from the substrate sampling probe30. In the exemplary embodiment depicted in FIG. 1, an electrosprayelectrode 64, which can comprise a capillary that is fluidly coupled tothe substrate sampling probe 30, terminates in an outlet end that atleast partially extends into the ionization chamber 12 and dischargesthe desorption solvent therein. As will be appreciated by a personskilled in the art in light of the present teachings, the outlet end ofthe electrospray electrode 64 can atomize, aerosolize, nebulize, orotherwise discharge (e.g., spray with a nozzle) the desorption solventinto the ionization chamber 12 to form a sample plume comprising aplurality of micro-droplets generally directed toward (e.g., in thevicinity of) the curtain plate aperture 14 b and vacuum chamber samplingorifice 16 b. As is known in the art, analytes contained within themicro-droplets can be ionized (i.e., charged) by the ion source 60, forexample, as the sample plume is generated. By way of non-limitingexample, the outlet end of the electrospray electrode 64 can be made ofa conductive material and electrically coupled to a pole of a voltagesource (not shown), while the other pole of the voltage source can begrounded. Micro-droplets contained within the sample plume can thus becharged by the voltage applied to the outlet end such that as thedesorption solvent within the droplets evaporates during desolvation inthe ionization chamber 12 such bare charged analyte ions are releasedand drawn toward and through the apertures 14 b, 16 b and focused (e.g.,via one or more ion lens) into the mass analyzer 70. As discussed below,in some aspects of the present teaching, the desorption solvent can becontinuously delivered to the ion source 60 during the stopped-flowcondition of the sampling interface so as to maintain the stability ofthe one or more pumping mechanisms and the ion source 60. Though the ionsource probe is generally described herein as an electrospray electrode64, it should be appreciated that any number of different ionizationtechniques known in the art for ionizing liquid samples and modified inaccordance with the present teachings can be utilized as the ion source60. By way of non-limiting example, the ion source 60 can be anelectrospray ionization device, a nebulizer assisted electrospraydevice, a chemical ionization device, a nebulizer assisted atomizationdevice, a photoionization device, a laser ionization device, athermospray ionization device, or a sonic spray ionization device. Itwill be appreciated that in some aspects, the ion source 60 canoptionally include a source of pressurized gas (e.g. nitrogen, air, ornoble gas) that supplies a high velocity nebulizing gas flow whichsurrounds the outlet end of the electrospray electrode 64 and interactswith the fluid discharged therefrom to enhance the formation of thesample plume and the ion release within the plume for sampling by 14 band 16 b, e.g., via the interaction of the high speed nebulizing flowand jet of liquid sample. The nebulizer gas can be supplied at a varietyof flow rates, for example, in a range from about 0.1 L/min to about 20L/min.

In the depicted embodiment, the ionization chamber 12 can be maintainedat an atmospheric pressure, though in some embodiments, the ionizationchamber 12 can be evacuated to a pressure lower than atmosphericpressure. The ionization chamber 12, within which analytes desorbed fromthe substrate 20 can be ionized as the desorption solvent is dischargedfrom the electrospray electrode 64, is separated from a gas curtainchamber 14 by a plate 14 a having a curtain plate aperture 14 b. Asshown, a vacuum chamber 16, which houses the mass analyzer 70, isseparated from the curtain chamber 14 by a plate 16 a having a vacuumchamber sampling orifice 16 b. The curtain chamber 14 and vacuum chamber16 can be maintained at a selected pressure(s) (e.g., the same ordifferent sub-atmospheric pressures, a pressure lower than theionization chamber) by evacuation through one or more vacuum pump ports18.

It will also be appreciated by a person skilled in the art and in lightof the teachings herein that the mass analyzer 70 can have a variety ofconfigurations. Generally, the mass analyzer 70 is configured to process(e.g., filter, sort, dissociate, detect, etc.) sample ions generated bythe ion source 60. By way of non-limiting example, the mass analyzer 70can be a triple quadrupole mass spectrometer, or any other mass analyzerknown in the art and modified in accordance with the teachings herein.Other non-limiting, exemplary mass spectrometer systems that can bemodified in accordance various aspects of the systems, devices, andmethods disclosed herein can be found, for example, in an articleentitled “Product ion scanning using a Q-q-Q_(linear) ion trap (Q TRAP®)mass spectrometer,” authored by James W. Hager and J. C. Yves Le Blancand published in Rapid Communications in Mass Spectrometry (2003; 17:1056-1064), and U.S. Pat. No. 7,923,681, entitled “Collision Cell forMass Spectrometer,” which are hereby incorporated by reference in theirentireties. Other configurations, including but not limited to thosedescribed herein and others known to those skilled in the art, can alsobe utilized in conjunction with the systems, devices, and methodsdisclosed herein. For instance other suitable mass spectrometers includesingle quadrupole, triple quadrupole, ToF, trap, and hybrid analyzers.It will further be appreciated that any number of additional elementscan be included in the system 10 including, for example, an ion mobilityspectrometer (e.g., a differential mobility spectrometer) that isdisposed between the ionization chamber 12 and the mass analyzer 70 andis configured to separate ions based on their mobility through a driftgas in high- and low-fields rather than their mass-to-charge ratio).Additionally, it will be appreciated that the mass analyzer 70 cancomprise a detector that can detect the ions which pass through theanalyzer 70 and can, for example, supply a signal indicative of thenumber of ions per second that are detected.

With reference now to FIG. 2, an exemplary substrate sampling probe 30(e.g., an open port probe) for desorbing one or more analytes from aSPME substrate 20 and suitable for use in the system of FIG. 1 isschematically depicted. Other non-limiting, exemplary samplingsubstrates that can be modified in accordance various aspects of thesystems, devices, and methods disclosed herein can be found, forexample, in an article entitled “An open port sampling interface forliquid introduction atmospheric pressure ionization mass spectrometry,”authored by van Berkel et al. and published in Rapid Communication inMass Spectrometry 29(19), 1749-1756, which is incorporated by referencein its entirety. As shown, the substrate sampling probe 30 is generallydisposed between the reservoir 50 and ion source 60 and provides a fluidpathway therebetween such that analytes entrained within desorptionsolvent that is provided by the reservoir 50 can be delivered to andionized by the ion source 60. The sampling probe 30 can have a varietyof configurations for sampling desorbed analytes from a substrate, butin the depicted exemplary configuration includes an outer tube (e.g.,outer capillary tube 32) extending from a proximal end 32 a to a distalend 32 b and an inner tube (e.g., inner capillary tube 34) disposedco-axially within the outer capillary tube 32. As shown, the innercapillary tube 34 also extends from a proximal end 34 a to a distal end34 b. The inner capillary tube 34 comprises an axial bore providing afluid channel therethrough, which as shown in the exemplary embodimentof FIG. 2 defines a sampling conduit 36 through which liquid can betransmitted from the substrate sampling probe 30 to the ion source 40 ofFIG. 1 via the probe outlet conduit 44 c (i.e., the sampling conduit 36can be fluidly coupled to the inner bore of the electrospray electrode64 via the fluid handling system 40). On the other hand, the annularspace between the inner surface of the outer capillary tube 32 and theouter surface of the inner capillary tube 34 can define a desorptionsolvent conduit 38 extending from an inlet end coupled to the desorptionsolvent source 50 (e.g., via the probe inlet conduit 44 b) to an outletend (adjacent the distal end 34 b of the inner capillary tube 34). Insome exemplary aspects of the present teachings, the distal end 34 b ofthe inner capillary tube 34 can be recessed relative to the distal end32 b of the outer capillary tube 32 (e.g., by a distance h as shown inFIG. 2) so as to define a distal fluid chamber 35 of the substratesampling probe 30 that extends between and is defined by the distal end34 b of the inner capillary 34 and the distal end 32 b of the outercapillary tube 32. Thus, the distal fluid chamber 35 represents thespace adapted to contain fluid between the open distal end of thesubstrate sampling probe 30 and the distal end 34 b of the innercapillary tube 34. Further, as indicated by the arrows of FIG. 2 withinthe sampling probe 30, the desorption solvent conduit 38 is in fluidcommunication with the sampling capillary 36 via this distal fluidchamber 35. In this manner and depending on the fluid flow rates of therespective channels, fluid that is delivered to the distal fluid chamber35 through the desorption solvent conduit 38 can enter the inlet end ofthe sampling conduit 36 for transmission to its outlet end andsubsequently to the ion source 60. It should be appreciated that thoughthe inner capillary tube 34 is described above and shown in FIG. 2 asdefining the sampling conduit 36 and the annular space between the innercapillary tube 34 and the outer capillary tube 32 defines the desorptionsolvent conduit 38, the conduit defined by the inner capillary tube 34can instead be coupled to the desorption solvent source 50 (so as todefine the desorption solvent conduit) and the annular space between theinner and outer capillaries 34, 32 can be coupled to the ion source 60(so as to define the sampling conduit).

As shown in FIG. 2, the desorption solvent source 50 can be fluidlycoupled to the desorption solvent conduit 38 via a supply conduit 44 bthrough which desorption solvent can be delivered at a selectedvolumetric rate (e.g., via one or more pumping mechanisms includingreciprocating pumps, positive displacement pumps such as rotary, gear,plunger, piston, peristaltic, diaphragm pump, and other pumps such asgravity, impulse and centrifugal pumps can be used to pump liquidsample), all by way of non-limiting example. Any desorption solventeffective to desorb analytes from a substrate 20 (e.g., a SPME device)and amenable to the ionization process is suitable for use in thepresent teachings. Similarly, it will be appreciated that one or morepumping mechanisms can be provided for controlling the volumetric flowrate through the sampling conduit 36 and/or the electrospray electrodeof the ion source 60, the volumetric flow rates selected to be the sameor different from one another and the volumetric flow rate of thedesorption solvent through the desorption solvent conduit 38. Asdiscussed in detail below with reference to FIG. 4, in some aspects,these different volumetric flow rates through the various channels ofthe substrate sampling probe 30 and/or the electrospray electrode 44 canbe independently adjusted (e.g., by adjusting the flow rate of anebulizer gas surrounding the discharge end of the electrosprayelectrode) so as to control the movement of fluid throughout the system10 and/or the surface shape of the desorption solvent at the open end ofthe sampling probe 30. By way of non-limiting example, the volumetricflow rate through the desorption solvent conduit 38 can be temporarilyincreased relative to the volumetric flow rate through the samplingconduit 36 such that the fluid in the distal fluid chamber 35 overflowsfrom the open end of the substrate sampling probe 30 to clean anyresidual sample deposited by the withdrawn substrate and/or to preventany airborne material from being transmitted into the sampling conduit36 (e.g., after withdrawal of a substrate, before the insertion ofanother substrate). In various aspects, the volumetric flow rate ofdesorption solvent into and within the sampling probe 30 can be stoppedupon insertion of the substrate so as to concentrate the desorbedanalytes in a smaller volume of desorption solvent, as discussedotherwise herein.

As shown in FIG. 2, an exemplary SPME substrate 20 having a coatedsurface 22 to which analytes can be adsorbed, as described, for example,PCT Pub. No. WO2015188282 entitled “A Probe for Extraction of Moleculesof Interest from a Sample,” the teachings of which are herebyincorporated by reference in its entirety, is schematically depicted asbeing inserted through the open end of the substrate sampling probe 30such that the coated surface 22 is at least partially disposed in thedesorption solvent (e.g., the desorption solvent within the distal fluidchamber 35). As shown in FIG. 2, by way of non-limiting example, theexemplary substrate 20 can comprise an extended surface 22 upon which aSPME extraction phase (e.g., layer) has been coated and to which one ormore analytes of interest can be adsorbed during extraction from asample. Upon the coated surface 22 being inserted into the distal fluidchamber 35, the desorption solvent within the distal fluid chamber 35can be effective to desorb at least a portion of the one or moreanalytes adsorbed on the coated surface 22 such that the desorbedanalytes can flow with the desorption solvent into the inlet of thesampling conduit 36. Substrates for use in systems and methods inaccordance with the present teachings are generally able to be at leastpartially inserted into a fluid pathway provided by a substrate samplingprobe 30 such that the desorption solvent provided thereby is effectiveto desorb one or more analytes of interest from the substrate, thoughthe substrate configuration (e.g., particles, fibers, blades,micro-tips, pins, or mesh) and/or coating (e.g., HLB-PAN, C18-PAN,antibodies, etc.) is not particularly limited. Indeed, any knownsubstrate and coating chemistries known in the art or hereafterdeveloped and modified in accordance with the present teachings can beused in the methods and systems disclosed herein. Other exemplary SPMEdevices suitable for use in accordance with various aspects of thepresent teachings are described, for example, in U.S. Pat. No.5,691,205, entitled “Method and Devise for Solid Phase Microextractionand Desorption,” the teachings of which are hereby incorporated byreference in their entireties.

It will be appreciated that substrate sampling probes in accordance withthe present teachings can also have a variety of configuration andsizes, with the substrate sampling probe 30 of FIG. 2 representing anexemplary depiction. By way of non-limiting example, the dimensions ofan inner diameter of the inner capillary tube 34 can be in a range fromabout 1 micron to about 1 mm (e.g., 200 microns), with exemplarydimensions of the outer diameter of the inner capillary tube 34 being ina range from about 100 microns to about 3 or 4 centimeters (e.g., 360microns). Also by way of example, the dimensions of the inner diameterof the outer capillary tube 32 can be in a range from about 100 micronsto about 3 or 4 centimeters (e.g., 450 microns), with the typicaldimensions of the outer diameter of the outer capillary tube 32 being ina range from about 150 microns to about 3 or 4 centimeters (e.g., 950microns). The cross-sectional shapes of the inner capillary tube 34and/or the outer capillary tube 32 can be circular, elliptical,superelliptical (i.e., shaped like a superellipse), or even polygonal(e.g., square). Additional details regarding SPME sampling probessuitable for use in the system of FIG. 1 and modified in accordance withthe present teachings can be found, for example, in U.S. Pub. No.20130294971 entitled “Surface Sampling Concentration and Reaction Probe”and U.S. Pub. No. 20140216177 entitled “Method and System for Formationand Withdrawal of a Sample From a Surface to be Analyzed” the teachingof which are hereby incorporated by reference in their entireties.

With reference now to FIGS. 3A and 3B, an exemplary fluid handlingsystem 40 in accordance with various aspects of the present teachings isdepicted in additional detail. As shown, the fluid handling system 40comprises a valve 41 fluidly coupled to the reservoir 50, the samplingprobe 30, and the ion source 60. It will be appreciated by a personskilled in the art that a pump (not shown) can additionally be providedso as to control the flow of fluid through the fluid handling system 40as otherwise discussed herein. In the depicted fluid handling system 40,the valve 41 comprises a four-way valve having a plurality of passages46 a,b that can be selectively coupled to the various inlets and outletsof the components of the system 10 in accordance with various aspects ofthe present teachings. In particular, the valve 41 in a firstconfiguration can provide a continuous fluid pathway from the reservoir50 to the ion source 60 via the sample space 35 of the sampling probe 30(FIG. 3A) and in a second configuration can provide a fluid pathway suchthat desorption solvent flows directly from the reservoir 50 to the ionsource 60 while bypassing the sampling probe 30 (e.g., without thedesorption solvent being delivered to the sample space 35) (FIG. 3B). Itwill be appreciated that actuating the valve 41 from the configurationof FIG. 3A to that of FIG. 3B, fluidly isolates the sampling probe 30from the reservoir 50 and ion source 60 such that the flow of desorptionsolvent within the sampling probe 30 would be substantially stopped.Nonetheless, the flow of fluid to the ion source 60 can continue whilethe valve is in stopped-flow configuration as shown in FIG. 3B, forexample, at substantially the same volumetric flow rate as in theconfiguration of FIG. 3A, thereby maintaining the stability of the ionsource 60 (e.g., the ion source does not need to be re-equilibratedfollowing a dry condition).

As shown in the exemplary depiction of FIGS. 3A and 3B, the valve 41 caninclude a plurality of passages 46 a,b, each of which is fluidly coupledto a fluid channel 44 a-d via a port 45 a-d. For example, in thecontinuous flow mode configuration of FIG. 3A, valve 41 provides a fluidpassage 46 a extending between the outlet channel 44 a of the reservoir50 and the inlet channel 44 b of the sampling probe 30 so as to providedesorption solvent to the desorption solvent conduit 38. After beingflowed through the sample space 35 and the sampling conduit 36, thedesorption solvent can then be transferred to the ion source 60 via theprobe outlet channel 44 c, the passage 46 b within the valve 41, and theion source inlet channel 44 d. In accordance with various aspects of thepresent teachings, the fluid pathways in the fluid handling system 40can be re-configured (e.g., during a step of desorption of analyte(s)from one or more substrates) to the stopped-flow mode configurationshown in FIG. 3B by actuating the valve 41 (e.g., manually orelectrically under the control of a controller). As depicted in FIG. 3B,for example, the passages 46 a,b and ports 45 a-d have been rotated 90°clockwise relative to the configuration shown in FIG. 3A such that thepassage 46 a directly connects the outlet channel 44 a of the reservoir50 and the ion source inlet channel 44 d (thereby bypassing the samplingprobe 30), while passage 46 b connects the inlet and outlet channels 44b,c of the sampling probe 30, thus forming a closed circuit within thesampling probe 30 having substantially no fluid flow.

With reference now to FIGS. 4A-D, these figures schematically representvarious conditions of the fluid flow within the sampling probe 30 thatcan be generated before, during, and after the sampling methodsdescribed herein. As shown in FIG. 4A, for example, prior to inserting asubstrate into the sampling space 35, the volumetric flow rate throughthe desorption solvent conduit 38 can be temporarily increased relativeto the volumetric flow rate through the sampling conduit 36 such thatthe fluid in the distal fluid chamber 35 overflows from the open end ofthe substrate sampling probe 30 to clean any residual sample depositedby a previously-inserted substrate and/or to prevent any airbornematerial from being transmitted into the sampling conduit 36 (e.g.,after withdrawal of a substrate, before the insertion of anothersubstrate). With reference now to FIG. 4B, a temporarily higher flowrate can also be used to generate a dome-shaped surface profile at theopen end such that, when the flow of fluid is within the sampling probe30 is stopped as otherwise discussed herein, the substrate 20 can beinserted into the desorption solvent in a direction generallyperpendicular to the axis of the sampling probe 30 a. In this manner, alarger area for contact with the surface to which analytes are adsorbedis provided, which can thereby increase the desorption efficiency. Withreference now to FIG. 4C, the sampling space 35 of the sampling probe 30can also be utilized in various aspects to react analytes with variousreagents added to the sampling space 35 during the stopped-flow mode. Byway of example, before, during, or after desorption of the analytes froma substrate, one or more reagents can be added to the sampling space 35so as to react with analytes adsorbed to the substrate 20 and/orpreviously desorbed therefrom that remain in the sample space.Alternatively or additionally, a plurality of substrates can be insertedwithin the sampling space during a single duration of the stopped-flowmode such that analytes from multiple substrates can be desorbed intosubstantially the same volume of desorption solvent within the samplespace 35. In other embodiments, the reagent itself may contain ananalyte of interest to be analyzed. In such cases, droplets may bedispensed into the sampling probe to be detected independent of whethera desorbed analyte has previously, or will be present within thesampling space. With reference now to FIG. 4D, following desorption inthe stopped-flow mode (as in FIG. 4B) or reaction within the samplingspace (as in FIG. 4C), the fluid handling system 40 can be switched backto its continuous flow mode configuration such that the analytes thatwere desorbed into the desorption solvent within the sampling space 35are delivered to the ion source as flow within the sampling probe isre-commenced. In certain aspects, a lower desorption solvent flow ratecan be temporarily selected, thereby creating a vortex-like surfaceprofile at the sampling probe's open end and resulting in increasedsensitivity and/or sharper peak shape of the MS-based analysis.

With reference now to FIG. 5, another exemplary sample analysis system510 in accordance with various aspects of the present teachings isdepicted. System 510 is similar to that discussed above with referenceto FIGS. 1-4 in that it includes a reservoir 550 that can be fluidlycoupled via a fluid handling system 540 to a sampling probe 530 and anion source 560 so as to generate ions from analytes desorbed from asample substrate 520 for analysis by the mass analyzer 570. As discussedotherwise herein, the fluid handling system 540 can be configured toterminate the flow of desorption solvent within the sampling spaceduring insertion of the sampling probe 520 therein.

As shown in FIG. 5, the exemplary system 510 can be automated (e.g.,under the control of a controller 580) and can include an actuationmechanism 504 (e.g., robotic arm, stage, electromechanical translator,step motor, etc.) that is coupled to a sample holder 502 so as to grip,hold, or otherwise couple to a the sampling substrate 520. One exemplaryrobotic system suitable for use in accordance with the present teachingsis the Concept-96 autosampler marketed by PAS Technologies). Under thecontrol of the controller 580 (e.g., without human intervention), forexample, the actuation mechanism 504 can be configured to transfer thesubstrate 520 through a complete sample preparation workflow including,for example, conditioning the substrate (e.g., coating or otherwisefunctionalizing the surface to enable extraction of an analyte ofinterest), extraction/enrichment of the analytes from the sample (e.g.,by immersing the coated surface in the sample, with or withoutvortexing), rinsing the extracted sample (e.g., by immersing thesubstrate 520 having analytes adsorbed thereto in H₂O so as to removesome interfering molecules, salts, proteins, etc.), and inserting therinsed substrate 520 within the sampling space of the substrate samplingprobe 530. As discussed otherwise herein, the substrate sampling probe530 is configured to desorb analytes from the substrate 520 utilizingthe desorption solvent provided from the reservoir 550, with thedesorbed analytes being entrained within the desorption solvent to theion source 560/mass analyzer 570 for ionization/mass spectrometricanalysis.

As shown in FIG. 5, the exemplary fluid handling system 540 can comprisea pump 543 configured to pump desorption solvent from the reservoir 550to the sampling space of the probe 530. In various aspects, the pump 543can be operatively coupled to the controller 580 such that thevolumetric flow rate of the desorption solvent from the reservoir to thesampling probe 530 (and within the sampling space) can be adjusted basedon one or more signals provided by the controller 580. By way ofexample, the controller 580 can be configured to terminate the flow ofdesorption solvent by the pump 543 upon insertion of the samplesubstrate 520 within the sample space. Additionally or alternatively,the controller can be configured to increase the volumetric flow rate ofdesorption solvent to the sampling space after removal of a samplingsubstrate 520 therefrom so as to temporarily overflow desorption solventthrough the open end of the sampling probe 530 before another substrate520 is inserted therein by the actuation mechanism 502.

As noted above, the system 510 is also shown to include a source 563 ofpressurized gas (e.g. nitrogen, air, or noble gas) that supplies a highvelocity nebulizing gas flow which surrounds the outlet end of theelectrospray electrode 564 and interacts with the fluid dischargedtherefrom to enhance the formation of the sample plume and the ionrelease within the plume for sampling by 514 b and 516 b, e.g., via theinteraction of the high speed nebulizing flow and jet of liquid sample.The nebulizer gas can be supplied at a variety of flow rates, forexample, in a range from about 0.1 L/min to about 20 L/min, which canalso be controlled under the influence of controller 580. In accordancewith various aspects of the present teachings, it will be appreciatedthat the flow rate of the nebulizer gas can be adjusted (e.g., under theinfluence of controller 580) such that the flow rate of desorptionsolvent from the sampling space (e.g., via sampling conduit 36 of FIG.2) can be adjusted based, for example, on suction generated by theinteraction of the nebulizer gas and the desorption solvent as it isbeing discharged from the electrospray electrode 564 (e.g., due to theVenturi effect). In this manner, the controller 580 can additionally oralternatively control the flow rate of the desorption solvent throughthe sampling probe in accordance with various aspects of the presentteachings by adjusting one or more of a pump and/or valve forcontrolling the flow rate of the nebulizer gas. By way of non-limitingexample, the controller 580 can be configured to terminate the flow ofdesorption solvent provided by the pump 543 and/or the flow of nebulizergas provided from the nebulizer source 563 (e.g., via one or morevalves) so as to substantially terminate the flow of desorption solventwithin the sampling space during insertion of the substrate 520 therein.

The ionization chamber 512, within which analytes desorbed from thesubstrate 520 can be ionized as the desorption solvent is dischargedfrom the electrospray electrode 564, is separated from a gas curtainchamber 514 by a plate 514 a having a curtain plate aperture 514 b. Asshown, a vacuum chamber 516, which houses the mass analyzer 570, isseparated from the curtain chamber 514 by a plate 516 a having a vacuumchamber sampling orifice 516 b. The curtain chamber 514 and vacuumchamber 516 can be maintained at a selected pressure(s) (e.g., the sameor different sub-atmospheric pressures, a pressure lower than theionization chamber) by evacuation through one or more vacuum pump ports518.

Now referring to FIG. 6, another embodiment is depicted of the presentteachings in which no sampling substrate is utilized. In thisembodiment, one or more analytes of interest are contained within aliquid sample 601, and one or more droplets of the liquid samplecontaining the one or more analytes of interest are deposited into thesampling probe. In such embodiments, the apparatus is similar to thatwhich has been described previously for use with the sampling substratewith the exception that the desorption solvent contained within theconduit 38 which is not involving in a desorbing an analyte from asubstrate is characterized as a delivery solvent travelling in adelivery solvent conduit 638. In such cases, the valve functions in asimilar fashion in which when operating in the second configuration, theone or more analytes contained within the one or more droplets can beallowed to concentrate in the sampling probe before the valve isswitched to the first configuration which allows the analytes to betransferred to the ion source and for analysis.

It will be appreciated in light of the present teachings that theexemplary methods and systems described can be utilized in an automatedprotocol and can reduce and/or eliminate the need for complex andtime-consuming sample preparation steps such as liquid chromatography.In accordance with various aspects of the present teachings, anactuation mechanism (e.g., robotic arm, stage, electromechanicaltranslator, step motor, etc.) can be utilized to deliver under thecontrol of a controller (not shown) and without human intervention oneor more substrates to the sampling space of the sampling probe, timedfor example to coincide with the configuration of the fluid handlingsystem 40 as described otherwise herein so as to increase the desorptionefficiency and/or sensitivity of the analytes that were adsorbed ontothe surface of the sample substrate 20.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting. While the applicant's teachingsare described in conjunction with various embodiments, it is notintended that the applicant's teachings be limited to such embodiments.On the contrary, the applicant's teachings encompass variousalternatives, modifications, and equivalents, as will be appreciated bythose of skill in the art.

What is claimed is:
 1. A method for chemical analysis, comprising:directing a flow of solvent through a solvent conduit to an ion sourcevia a sampling space of a sampling probe, said sampling space being atleast partially defined by an open end of the sampling probe;terminating the flow of solvent into the sampling space from the solventconduit for a first duration; adding one or more analytes of interest tothe solvent contained within the sample space during said firstduration; reacting said analyte of interest with one or more reagentswithin the sample space during said first duration so as to formreaction products; and following the first duration, directing a flow ofsolvent containing said one or more reaction products from the samplingspace to an ion source.
 2. The method of claim 1, further comprisingadding said one or more reagents to the sample space during said firstduration.
 3. The method of claim 1, further comprising continuouslydelivering fluid to the ion source during said first duration.
 4. Themethod of claim 3, wherein continuously delivering fluid to the ionsource during said first duration comprises directing a flow of thesolvent from a reservoir to the ion source while bypassing the samplespace.
 5. The method of claim 4, wherein a valve for directing the flowof solvent through a plurality of fluid pathways is disposed between thereservoir and the sample space, and wherein directing the flow ofsolvent through the solvent conduit to the ion source via the samplespace comprises actuating the valve from a first configuration to asecond configuration.
 6. The method of claim 4, wherein a first fluidpathway is provided for flowing solvent from said reservoir to said ionsource via said sample space and a second fluid pathway is provided forflowing the solvent from said reservoir to said ion source and thatbypasses said sample space.
 7. The method of claim 1, wherein adding ananalyte of interest comprises inserting at least a portion of asubstrate having one or more analytes adsorbed thereto into the solventcontained within the sample space such that at least a portion of saidabsorbed analytes are desorbed from the substrate into the solvent. 8.The method of claim 7, wherein the substrate comprises one of asolid-phase microextraction substrate and surface functionalizedparticles.
 9. A system for analyzing a chemical composition of aspecimen, comprising: a reservoir for storing a solvent; a samplingprobe having a solvent conduit and a sampling conduit in fluidcommunication with one another via a sample space, said sampling spacebeing at least partially defined by an open end of the sampling probeand configured to receive solvent from the reservoir via the solventconduit; a fluid handling system comprising at least one pump and atleast one fluid pathway for delivering solvent from the reservoir to theion source; and a controller operatively coupled to the at least onepump and configured to control the volumetric flow rate of solventwithin the at least one pathway, wherein the controller is furtherconfigured to: terminate the flow of solvent from the solvent conduitinto the sampling space during a first duration, wherein the samplingprobe is configured to receive through the open end one or more analytesof interest into solvent contained within said sampling space duringsaid first duration; and following said first duration, direct a flow ofsolvent containing said one or more analytes of interest from thesampling space to the ion source via the sampling conduit.